Isolated metastatic amebic lung abscesses may occur de novo without obvious infection of the liver and may involve any part of the lung, including the apices. These abscesses are not always associated with pleural fluid and the diaphragm may be entirely normal. They are clinically and radiologically indistinguishable from any other lung abscesses; they can have thick or thin walls, may contain fluid, or be relatively solid. They may be single or multiple. Only their response to treatment provides a clue to their origin, unless they rupture into the bronchus and amebae can be identified in the sputum. The prognosis is good if treatment is instituted early and maintained, but there may be considerable residual lung fibrosis with bronchial deformity and stenosis.

A fistula to a bronchus occurs in 35% of all thoracic complications, basically communicating the hepatobiliary tract, or occasionally the pleura, chest wall and skin, with the bronchial tree (Fig. 1.99, A & B). Bilioptysis is not an uncommon symptom. Other etiologies of bronchobiliary fistula include hydatid disease, trauma, biliary obstruction, and subphrenic abscess. Cutaneous fistulas can also develop outward to the skin through the pleura. Secondary involvement of the ribs from an amebic empyema can occur (Fig. 1.99 C).

Identical events may occur in either side of the chest, but are much less common on the left (Figs. 1.92C & 1.93). There are no specific radiological features on the left side, other than the recognition of an enlarged left lobe of the liver and an associated pleural effusion in many patients. Perforation into the pericardium is an acute emergency, resembling a myocardial infarct and causing pericardial tamponade (Fig. 1.100). Pneumopericardium may complicate an abscess, which originated in the liver and has extended into the pericardium after first involving the lung or stomach (Fig. 1.101). An acute pericardial effusion in a patient with a fixed liver, but without a history suggesting a subphrenic abscess (such as from previous surgery), should lead to consideration of an amebic infection. The condition is so acute that it is unlikely to be a radiological problem. The end result may be constrictive pericarditis.

The diagnosis of thoracic amebiasis depends on the combination of a significantly elevated diaphragm on the affected side, hepatomegaly, and pleural effusion. Without these changes it is impossible to distinguish thoracic amebiasis from pulmonary infarction, pneumonia, pyogenic lung abscess, tuberculosis, or even malignancy.

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Fig. 1.99 Other complications of intrathoracic amebiasis. (A) A bronchopleural-cutaneous fistula involving the bronchus to the posterior basilar segment of the right lower lobe is visualized by injection of the cutaneous fistulous tract with iodinated contrast media. (B) PA chest film of the same patient, showing elevation of the right hemidiaphragm and persistent chronic pleural and parenchymal inflammatory changes at the right base. (C) Periostitis involving the lateral aspects of several left lower ribs, which developed from drainage of pus through a fistula in a patient with amebic empyema.

Fig. 1.100 Pericardial effusion with enlargement of the cardiac-pericardial silhouette, secondary to rupture of a left hepatic amebic abscess into the pericardium of a Mexican patient. (Courtesy of Drs. Kenji Kimura and Miguel Stoopen, Mexico City).

Fig. 1.101 Pneumopericardium in two Mexican patients (A and B). An amebic abscess from either the right or left lobe of the liver, or even from the lung, may rupture into the pericardium and cause acute tamponade, usually resulting in death. Occasionally, pneumopericardium will be seen if a lung abscess has extended into the pericardium or if an abscess in the left hepatic lobe has perforated through the stomach into the pericardium. (Courtesy of Dr. Jorge Ceballos-Labat, Mexico City).